The proposed work represents an effort to study various aspects of the endocrinology of aging. Areas to be investigated include: relationship between gonadol hormone level and sexual behavior in the rat; effect of age on vitamin D receptors in intestinal calcium absorption in the rat; the cause of the deterioration in glucose tolerance associated with age; the effect of age on somatomedin concentrations, binding and action; relationship between age, glucose intolerance, and glycosylated hemoglobin concentrations.